Mumps virus is one of several paramyxoviruses that have been increasingly implicated in a number of acute, subacute, and chronic central nervous system diseases of man. Several animal models now exist for the study of these infections. The current study represents an attempt to correlate observed in vivo and in vitro differnces in the biological behavior of several strains of mumps virus with presumed differences in their polypeptide composition. Three prototype strains of mumps virus, one adapted to growth in suckling hamster brain (neuroadapted), a low tissue culture passage isolate from a case of human mumps infection (wild) and a vaccine (Jeryl Lynn) derived strain, will be compared. The diverse biological effects of these strains will be studied in tissue culture and in animal pathogenesis studies. Through immunohistologic technics we will explore the differences in the distribution of viral antigens between the acute or productive and chronic or persistent phase of mumps virus encephalitis in the animal model system. Because of the many similarities of the various paramyxoviruses, the findings in the careful evaluation of this animal model system should further our understanding of other agents of this virus group.